Accoya wood

'Accoya' is being hailed as a
'new wood species'. John Alexander
of Accsys Technologies, suppliers of Accoya,
introduces this innovative form of wood treatment.

Introduction

Accoya® wood represents a major development in wood technology and enables the consistent supply of durable, dimensionally stable, non-toxic solid wood. An ideal material for manufacture of high performance exterior timber products. Accoya is based on the Acetylation of plantation grown softwood, the gold standard in the academic field of wood science for over 80 years. A break-through in closed-loop engineering, culminating in 2007, lead to the first commercial scale production of the product in the world. Critically, this high performance product is competitively priced to traditional hardwood options and widely available.

Accoya performance in exterior timber applications is well documented following decades of exterior field trials at research institutes around the world. The commercial product has been accredited with the same performance by BBA, BRE, TRADA and the Centre for Timber Engineering at Napier University.

The technology involved

The technology behind Accoya is based on wood acetylation, a process that has been studied since the first acetylation of pine to isolate lignin in 1928.

The physical properties of any material are determined by its chemical structure. Wood contains an abundance of chemical groups called “free hydroxyls”. Free hydroxyl groups absorb and release water according to changes in the climatic conditions to which the wood is exposed. This is the main reason why wood swells, shrinks and decays.

Acetylation effectively changes the free hydroxyls within the wood into acetyl groups. This is done by reacting the wood with acetic anhydride, which comes from acetic acid (commonly known as vinegar when in its dilute form). When the free hydroxyl group is transformed to an acetyl group, the ability of the wood to absorb water is greatly reduced, rendering the wood more dimensionally stable and extremely durable.

Acetyl groups, which are simply comprised of oxygen, hydrogen and carbon, are already naturally present in all wood species. This means that the manufacturing process adds nothing to the wood that does not already naturally occur. The end product, Accoya, is 100% non toxic. Incidentally, the only by-products from the manufacture of acetic anhydride are a small amount of valuable fertiliser and trace amounts of acetic acid which can be biodegraded.

Accoya has the same appearance as unmodified timber

Accoya in the context of other treated timbers

The effect of altering the wood’s chemical structure, as opposed to merely altering its chemical content, is essentially to create a type of wood. By contrast, virtually all other treatments merely insert chemicals (such as oils, biocides or metal compounds) into the cell walls of the wood.

Benefits

• 60 year minimum service life [BS8417] for joinery & cladding.
• At least 3x more dimensionally stable than any other timber.
• Upto 12 years maintenance for factory applied coatings.
• Accoya wood is easy to process and presents no problems to product manufacturers.
• Accoya wood is modified to the core and requires no end treatment on cut ends.
• 100% non toxic. Off-cuts can be recycled, burnt or composted.
• All Accoya is produced from plantation grown pine trees including FSC material.

Applications

Accoya is suitable for all exterior wood applications where long life, low maintenance and a low whole life cost are required. Most frequent usage in the UK is for windows, doors and cladding. But applications do not end there as balconies, decking, platers and boats have all been made from Accoya by British companies. Bridges are also being constructed. The largest in The Netherlands open in Autumn ’08 and support 2 lanes of traffic across a 30 metre span. The bridge has a design life of 80 years.

Specification

Accoya should be specified in conjunction with the large number of companies manufacturing cladding and joinery from Accoya.